It’s possible to add the confirmation box, but it won’t be working correctly. That’s because ACF won’t check if you click the “OK” or “Cancel” button so it will delete the layout no matter which one you click.
You can check how it works in “wp-content/plugins/advanced-custom-fields-pro/pro/assets/js/acf-pro-input.js” on line 1086.
If you want, you need to add the confirmation code in the core file (acf-pro-input.min.js).
I hope this helps 🙂
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